Hydration-alkylation process



v 1966 R. B. MOSELY HYDRATION-ALKYLATION PROCESS Filed Jan. 1'7, 1965 2.555 was; :22; 3:8: 2 q ITJ 2 a: :2 n g 2 8 an 3 e2 2 INVENTOR ROBERT B. MOSELY =W4 W HIS ATTORNEY United States Patent 3,250,822 HYDRATION-ALKYLATIGN PROCESS Robert B. Mosely, Walnut Creek, Calih, 'assignor to Shell Oil Company, New York, N.Y., a corporation of Delaare Filed Jan. 17, 1963, Ser. No. 252,179 6 Claims. (Cl. 260683.49)

This invention relates to a process for converting normal and iso-olefin into high octane gasoline components.

Although of recent times, catalytic reforming of various gasoline boiling hydrocarbon fractions has come into relatively wide use, a main source of premium grade motor gasoline has been from catalytically cracking higher boiling oils. The octane number of premium gasoline has steadily increased and this has required the use of more and more catalytically cracked gasoline to meet octane requirements. Furthermore, severity of catalytic cracking has been increased to produce catalytically cracked gasoline having the highest possible octane number consistent with permissible losses.

In the practice in the past, higher boiling hydrocarbon oils have been catalytically cracked to produce gasoline along with gaseous products including propylene and butylene. The common practice was to polymerize a propane-propylene fraction from a catalytic cracking unit and blend the resulting polymer in gasoline. Furthermore, it has been the practice to alkylate a butylene fraction with isobutanes to produce alkylate which is also blended with catalytically cracked gasoline. These operations have not been entirely satisfactory for several reasons. In the first place, when effecting the catalytic cracking under severe conditions to produce a gasoline having a high octane number, it has been found that the gasoline so produced has a sensitivity higher than desired. (Sensitivity is an inverse function of the gasolines ability to maintain its resistance to detonation as engine operating conditions become more severe, e.g., on the road, from city-type driving to high-speed, freeway-type driving. The sensitivity of a fuel is defined quantitatively as the dilference between research and motor octane numbers.) This condition has been further aggravated by the polymer produced and blended in the gasoline. The increased sensitivity of these more severely cracked hydrocarbons has been attributed, to a large extent, to the greater amount of olefins produced. In addition, anti-smog legislation has been proposed, in certain areas, to reduce the amount of olefins in gasoline.

It has been suggested that the higher molecular weight olefins in the catalytically cracked gasoline such as C and heavier olefins be alkylated in the presence of conventional mineral acid catalysts. However, alkylation has not been the best solution since mineral acid alkylation of a catalytically cracked C /C fraction, which contains alarge amount of diolefin, results in uneconomically high acid consumption.

Another process which has been practiced is the hydrogenation of catalytically cracked gasoline. Hydrogenation of the gasoline has been unsatisfactory because, while there has been a gain in sensitivity control as a result of saturation of the olefins to paraflins, there has been a substantial loss in research octane number. Therefore, it has been a practice to hydrogenate this stream only partially (40-60% conversion) which has resulted in some improvement in sensitivity with only small loss, when compared to total hydrogenation, in research octane number.

These disadvantages are largely overcome by the combination process of the present invention, which provides a blended gasoline having a high octane number and low sensitivity. According to the invention, a mixture of normal and iso-olefins having from 5 to 7 carbon atoms,

3,250,822 Patented May 10, 1966 such as a light, catalytically cracked fraction, is selectively hydrated under acid conditions to produce a mixture of predominantly tertiary alcohols. The unreacted hydrocarbon fraction containing normal and secondary olefins is recovered from the hydration unit and is subsequently processed to produce a fraction rich in isoparaffins. These and additional advantages of this process will be ap parent as the invention is described with reference to the drawing which shows a preferred embodiment of the invention.

The invention is broadly applicable to a mixture of normal and iso-olefins having from 5 to 7 carbon atoms. It is particularly applicable to gasoline fractions containing C to C normal and iso-olefins obtained from the cracking of hydrocarbon oils.

In order to set forth more fully the nature of the in vention, without however intending to limit the scope of the invention, it will be described in detail as applied to the selective hydration, under sulfuric acid conditions, of a C to C catalytically cracked fraction and the subsequent alkylation to isoparafiins of the normal olefins in the unreacted hydrocarbon fraction.

Referring now to the drawing: a C to C fraction 'containing normal and iso-olefin is introduced into reactor 12 via line 14 wherein it is contacted with sulfuric acid added through line 16. Auxiliary equipment such as pumps, heat exchangers, valves, control mechanisms, etc., which are obvious to those skilled in the art are not shown. The hydrocarbon can be contacted with acid in a single reactor. However, it is preferred to employ a plurality of reactors in order to approach equilibrium conditions. For example, when employing two reactors, efiiuent from reactor 12 enters reactor 18 via line 20. The reactors can be of suitable design such as stirred reactors or can be of the tower reactor design with or without contacting means such as perforated trays. Iso-olefins are selectively hydrated with sulfuric acid of from about 40% to about concentration, preferably from about 50% to about 70% concentration. The hydration temperature can be in the range of from about 0 C. to about 30 C., preferably from about 0 to about 20 C. The ratio of acid to hydrocarbon is from about 1:3 to about 3:1, preferably about 1:1.

A hydrocarbon-acid mixture is Withdrawn from reactor 18 and enters settler 22 through line 24. Settled acid is Withdrawn and recycled via line 16. A hydrocarbon phase containing alcohol and entrained acid is withdrawn from the settler and introduced into water-wash settler 26 through line 28. At the low hydration temperatures, the tertiary C and heavier alcohols are soluble in the hydrocarbon phase while the majority of the tertiary C alcohols initially produced remain in the acid phase and are recycled with the acid. As the amount of tertiary C alcohols builds up in the acid phase, more of the tertiary C alcohols produced by isoolefin hydration will be withdrawn in the hydrocarbon phase with, of course, the tertiary C and heavier alcohols, until equilibrium is obtained, when substantially all of the tertiary C alcohols thereafter produced will be Withdrawn in the hydrocarbon phase. Water is introduced into the water-wash settler through line 30. While it is not necessary in the practice of the invention, it is preferred to use only a minimum amount of water, usually the stoichiometric amount necessary to convert the olefin to alcohols, in order to minimize water handling and concomitant corrosion problems. It is desirable, when using this small amount of water, to use multiple contacting stages for greater washing efficiency. When using only the stoichiometric amount of water for washing, the water, containing acid, is withdrawn via line 31, combined with the acid from settler 22, and recycled to the reaction Zone. Sulfuric acid can be added to the system as necessary.

Hydrocarbon is withdrawn from water-wash settler 26 via line 32, given a caustic wash in vessel 34 to neutralize any entrained acid and introduce into fractionation tower 36 through line 38 wherein alcohol is separated from unreacted hydrocarbon. An alcohol fraction is withdrawn as a bottom product and is routed to alcohol storage vessel 40 through line 42. A fraction containing normal and secondary olefins is recovered as an overhead product via line 44.

The synthesis of alcohols by the hydration of olefins can be carried out by other processes such as by contacting the olefin with water in the presence of an organic ion exchange material (of the sulfonated resin type), a catalytic system comprising hydrogen fluoride and boron trichloride, a supported phosphoric acid catalyst, oxides or sulfides of tungsten on a carrier, etc.

The fraction containing normal and secondary olefins from the hydration process is passed to alkylation reactor 50 together with isobutane from line 52.

It is of importance in alkylation processes that the hydrocarbon mixture in the alkylation zone contain a substantial excess of the isoparaflins. Thus, the external isoparafiin olefin ratio is usually maintained between 3.5 :1

and 8:1 in sulfuric acid alkylation, and even higher, e.g., between 6:1 and 12-21, in HF alkylation. The internal isoparaffin olefin ratio is preferably at least 300:1 and 'may be as high as 800:1 or more. Since the isoparafiin is present in the alkylation zone in excess of that required for the reaction,'a substantial amount remains unconverted while practically all of the olefin is combined with isoparaffin. Since other hydrocarbons such as normal paraffin, and even the alkylate product itself, act as a diluent for the isobutane and olefin reactants, perhaps, a better indication of proper alkylation conditions is the percent of isobutane in the reactant efiluent. Thus, it is generally desired to operate with an isobutane content in the reactor hydrocarbon eflluent of about 50% and higher. However, operation can be effected at lower isobutane contents if accompanied by low olefin feed rates. The liquid hydrocarbon flows downwardly through the reaction vessel, passing through particulate contact bed 54 which is wetted with alkylation acid. fraction can, of course, be carried out in conventional processes using acid emulsions.)

The contact bed should consist of inert material, i.e., the material should not react with the liquids to be passed therethrough. The surface of the contact bed should be hydrophilic so that it is preferentially wetted by the acid catalyst. The alkylation acid is thereby retained on the surface of the contact bed and in this way, a large contact surface-is formed. Examples of contact material suitable for use in carrying out the process according to the invention are ceramic materials, lava, glass, gravel, ion exchange resins such as one of the sulfonated polystyrene type coke-breeze and the like. The contact material may have the form of Raschig rings, Berl saddles, Dixon packing, beads or fibers. The particle size of this contact material can vary from about 0.1 mm. to about 30 mm., preferably from about 0.5 to about mm.

The contactbed is contained in a suitable reactor vessel such as a sphere, cylindrical tower, or the like. The contact material is suitably supported within the vessel by means such as perforated plates, screens, grids, and the like. It is generally preferred to provide a space above and below the contact bed to provide room for liquid distributor heads, separation and collecting zones, and the like.

The alkylation catalyst is a strong mineral acid such as sulfuric acid or anhydrous hydrofluoric acid. The titratable acidity of the sulfuric acid employed as catalyst in the alkylation reactor is generally in the range from 85% to 100% H 80 and preferably between 88% and 98% H 80 It is general practice to charge to the process sulfuric acid having between 96% and 100% concentra tion and to use it until its titratable acidity has dropped to a lower value, e.g., about 85 to 90%. The concentration of hydrofluoric acid used as an alkylation catalyst is between 80% and 100%, and suitably between 86% and 90%, care being taken to keep water out of the reaction system. i

The alkylation reaction is carried out at temperatures in the range of from 0 C. to about 22 C. and preferably from 4 C. to 16 C. and pressures in the range from atmospheric to 135 p.s.i.g., but sutficiently high to maintain the reactants in liquid phase. Alkylation with anhydrous HF catalyst can be carried out at somewhat higher temperatures than the sulfuric acid catalyst and is generally between 0 C. and 65 0., preferably between 25 C. and

(The alkylation of this It is important that a small amount of acid relative to the amount of hydrocarbon be maintained within the reaction zone. Within the reaction zone then, the total amount of acid relative to the amount of hydrocarbon should be from about 0.05:1 to about 0.411 and preferably from about 0.121 to 0.25:1 on a volume basis.

The total amountof acid within the reaction zone includes the amount of acid holdup by the contact material as well as any recycle acid passing through the bed. It is preferred to introduce recycle acid via line 56 into the reactor above contact bed 54 and pass recycle acid through the bed with the hydrocarbon to assure that suflicient acid is present to wet the entire bed of contact material. Moreover, the recycle acid, in flowing across the surface of the contact material as a thin film, serves to renew the acid on the contact material. Even though recycle acid tends to increase the thickness of the acid film on the support, no adverse effect on yield or selectivity is observed. Thus, the amount of recycle acid can vary considerably as long as the total amount of acid in.

the reaction zone is within the prescribed limits. For example, with glass beads where the amount of acid holdup is relatively small, i.e., 2.55% v., the amount of excess acid which is recycled through the bed can be as high as two to three times the amount of acid holdup on the beads. Usually the amount of recycle acid is less than about 25%, preferably less than about 20%, of the residual interstitial volume of the contact material after the contact material is wetted with a film of acid. The residual volume is often inconvenient to determine, therefore, it is preferred that the amount of excess acid recycled to the contact bed be from about 0.01 to 0.3 part by volume, and preferably from about 0.05 to 0.2 part by volume, per part by volume of hydrocarbon feed.

The alkylation acid and hydrocarbon flow con-currently and downwardly through the contact bed and into a settling zone. The flow of two immiscible liquids through such a bed is described in Beningh, U.S. Patent 3,014,864, December 26, 1961. The alkylation acid, draining by gravity from the bed and being stripped from the contact material by the moving hydrocarbon, leaves the contact bed as liquid droplets which are rather large in diameter and, being of greater density than the hydrocarbon liquid, readily fall to the bottom of the settling zone 58 where the droplets accumulate as a pool of acid. The acid is withdrawn from the reaction vessel through line 60 and is recycled to a point above the contact bed via line 56. Fresh acid is added to the system as necessary. Spent acid is withdrawn through line 62. When sulfuric acid is used as the catalyst in both the alkylation and hydration processes, a portion of the spent alkylation acid can be diluted with water to hydration acid strength, and routed via line 64 volume of recycle hydrocarbons, the temperature rise within the reaction zone is maintained within the desirable limits. Moreover, recycling large volumes of hydrocarbon through the reaction zone provides additional overall contact time which permits any olefins which are not reacted during the initial pass through the reaction zone to be alkylated in the subsequent passes. Consequently, a proportion of the hydrocarbon from line 66 is returned to the reactor via line 68.

The contact time for the alkylation reaction can be provided by recycling a part of the hydrocarbon over the contact bed. Contact time can also be increased by lowering the velocity of the hydrocarbons through the contact bed by increasing the amounts of acid per unit of space (which can be done for example by comprising a contact material of smaller particle size) or by increasing the depth of the contact bed. Contact times of about five to thirty-five minutes are preferred but can be varied depending upon the type of apparatus, contact bed, nature of olefin feed and the like, from about a minute to as much as 60 minutes.

The amount of hydrocarbon recycle can vary over a wide range as to achieve the desired contact time. Recycle is conveniently expressed as the volume of recycle hydrocarbon per volume of olefin feed and preferably is in the range from to about 1500 although the recycle can vary as low as one and as high as 60,000. Too high a recycle rate is not only undesirable from the standpoint of equipment and operating costs but can lead to excessive velocities through the contact bed. Hydrocarbon velocity through the contact bed is generally limited to no more than about one-foot per second. Although velocities somewhat above this limit can be used, in general it may tend to create excessive pressure drop through the bed, cause excessive stripping of the acid catalyst from the inert solid and can lead to the formation of undesirable emulsions.

The remaining liquid hydrocarbon is passed to fractionation tower 70 wherein isobutane is separated from the reaction products (generally called alkylate) and is recycled to reactor 50 via line 52. Isobutane is added to the system as necessary. Alkylate is withdrawn from the bottom of the fractionation tower via line 72. It is generally desirable to give the alkylate a caustic and water wash to remove any residual acidity.

Alkylate is routed through line 72 into gasoline blending tank 74. Alcohol from storage vessel 40 and is routed through line 76 into gasoline blending tank 74. A portion of the alcohol can be purified and routed to other storage for sales as chemicals, etc.

The following examples are illustrative of some of the advantages derived from the invention, but are not to be considered to limit the scope of the invention.

EXAMPLE I The benefits derived from selectively hydrating a catalytically-cracked fraction containing C through C normal and iso-olefins under acid conditions to produce a mixture of predominantly tertiary alcohols is seen from a comparison of the component blending octane numbers of tertiary amylenes and tertiary amyl alcohol given below in Table I.

The sensitivity of the alcohol relative to the corresponding olefin is considerably lower. The sensitivity of the alcohol is reduced markedly by the addition of 3 ccs. tetraethyl lead per gallon of fuel. However, the sensitivity of the olefin is unaffected by addition of lead. It is a particularly attractive expedient to adjust hydration conditions to selectively hydrate the isoolefins to tertiary alcohols because the secondary and primary alcohols have sensitivities not substantially different from their olefinic counterparts.

EXAMPLE II The removal of the iso-olefin from alkylation feed results in increased acid life. A comparison of carbon formation in sulfuric acid catalyst used in alkylating various olefins under comparable conditions is shown in Table II.

Acid life is an inverse function of an amount of carbon in the acid phase (e.g., acid life decreases as carbon in acid phase increases).

Carbon formation in the acid catalyst is from about two to about four times greater when the olefin feed is '2-methyl-2-butene than when it is l-pentene or 3-methyll-pentene. Therefore, the removal of certain diand iso-olefins in the hydration process increases the acid lift of a feed containing normal olefins.

EXAMPLE III The isoolefins which are selectively hydrated to tertiary alcohols, e.g., Z-methyl-l-butene and Z-methyl-l-pentene, form two to three times as much heavy alkylate as the normal and secondary (e.g., 4-methyl-1-pentene) olefins which are not hydrated under the selective conditions. A comparison of alkylate produced by various olefins under comparable sulfuric acid alkylation conditions is shown in Table III and Table IV.

Table III COMPARISON OF PENTENES AS ALKYLATION FEED 1 l-pentene 2-methy1-1-butene Olefin, LHSV 0. 14 0. 013 0. 16 0. 013 Percent V. i'C4H in 0.1+". 43 42 40 41 Acid/BIC, v./v 0.21 0.23 0. 22 0.23

Products, percent w.:

Table IV COMPARISON OF HEXENES AS ALKYLATION FEED l-hexene 4 methyl-1- Q-methyl-I-pentene pentene Olefin, LHSV 0.15 0. 015 0. 17 0.017 Percent v. i-CtH in Cr+ 44 59 57 62 Products, percent w.:

C5- 1 94.0 97.0 82.9 93.0 Cu 6.0 3.0 17.1 7.0

As the heavy alkylate is a less valuable refinery product than either the tertiary alcohols produced from the selective hydration of tertiary olefin or the light alkylate .7 produced from the alkylation of the normal and secondary olefin the combination process of the invention results in an improved motor gasoline blend.

I claim as my invention:

1. A process for the conversion of a mixture of normal and isoolefins having from 5 to 7 carbon atoms which comprises in combination:

(1) passing the mixture into a hydration zone containing a hydration catalyst under conditions conducive to the selective hydration of iso-olefin to tertiary alcohol;

(2) recovering tertiary alcohol and a fraction containing normal olefin;

(3) passing the fraction containing normal olefin together with an isoparaffin into an alkylation zone containing a strong mineral acid alkylation catalyst selected from the group consisting of H SO and HF at alkylation conditions; and

(4) recovering alkylate from the alkylation zone effiuent.

2. The process according to claim 1 wherein the hydration catalyst is sulfuric acid having a concentration of from about 40% to about 80% and the hydration conditions comprise a temperature in the range of from about C. to about 30 C.

3. The process according to claim 1 wherein the hydration catalyst is sulfuric acid having a concentration of from about 50% to about 70% and the hydration conditions comprise a temperature in the range of from about 0 C. to about 20 C.

' 4. The process according to claim 1 wherein the strong mineral acid alkylation catalyst is sulfuric acid and the alkylation conditions comprise a temperature in the range of from about 0 to about 20 C.

5. The process according to claim 1 wherein the strong 8 mineral acid alkylation catalyst is hydrofluoric acid and the alkylation conditions comprise a temperature in the range of from about 0 to about C. A 6. A process for conversion of a catalytically-cracked gasoline fraction having 5 to 7 carbon atoms per molecule which comprises:

(1) passing the fraction into a hydration zone containing sulfuric acid having a concentration of from about 40% to and selectively hydrating isoolefin to tertiary alcohol at a temperature of 0 to about 20 C.; v (2) recovering tertiary alcohol and a fraction containing normal olefin; (3) passing the fraction containing normal olefin together with isoparaffin at alkylation conditions of 0 C. to about 22 C. into an alkylation zone containing sulfuric acid having a concentration of from about to and (4) recovering alkylate from the alkylation zone.

References Cited by the Examiner UNITED STATES PATENTS 1,907,309 5/1933 Van Schaack 44-56 2,070,258 2/1937 Coleman et al. 260641 2,255,275 9/1941 Stahly 44-56 2,427,293 9/ 1947 Matuszak 260-68361 X 2,574,325 11/1951 Gislon et al. 260-641 2,894,998 7/1959 Hess et al. 260-683.61 2,962,537 11/1960 Peters et al. 260-641 X 3,050,456 8/1962 Melchior 260683.61 X

DELBERT E. GANTZ, Primary Examiner.

DANIEL E. WYMAN, Examiner.

c. o. THOMAS, R. H. SHUBERT, Assistant Examiners. 

1. A PROCESS FOR THE CONVERSION OF A MIXTURE OF NORMAL AND ISOLEFINS HAVING FROM 5 TO 7 CARBON ATOMS WHICH COMPRISES IN COMBINATION: (1) PASSING THE MIXTURE INTO A HYDRATION ZONE CONTAINING A HYDRATION CATALYST UNDER CONDITIONS CONDUCIVE TO THE SELECTIVE HYDRATION OF ISO-OLEFIN TO TERTIARY ALCOHOL; (2) RECOVERING TERITARY ALCOHOL AND A FRACTION CONTAINING NORMAL OLEFIN; (3) PASSING THE FRACTION CONTAINING NORMAL OLEFIN TOGETHER WITH AN ISOPARAFFIN INTO AN ALKYLATION ZONE CONTAINING A STGRONG MINERAL ACID ALKYLATION CATALYST SELECTED FROM THE GROUP CONSISTING OF H2SO4 AND HF AT ALKYLATION CONDITIONS; AND (4) RECOVERING ALKYLATE FROM THE ALKYLATION ZONE EFFUENT. 